Hi Manohardas. I also in fact studied hard to enter into IIST, Trivandrum but just missed the cutoff. So, I hope I will be able to help you in this regard.

Now, IIST is one among the few institutions in India that take admissions to their B.Tech programs on the basis of the students JEE Advanced rank. 

The application form of IIST is generally released a few days after the JEE Advanced paper.

In the year 2018, IIST B.Tech 2018 application forms will be released on May 22, 2018 in an online mode. The last date for filling it is on June 5, 2018.

I would advice you to prepare intensively for JEE Advanced as the institute only takes in 140 students for all its programs (yes, just 140!).

For more, I would please advice you to see this link:

• https://engineering.careers360.com/articles/iist-btech-admission

Hope this helps you and all the best!